2073850 - Debug assertion: culling rect loses part of the screen; pinch to zoom at large offset

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[Thomas Nibler [:tnibler]]

Attachment: pinch-zoom-assert.html

[2771401] Hit MOZ_CRASH(vis culling rect Box2D((26.666664, 598582.2), (1717.3331, 600431.06)) loses part of the screen Box2D((0.0, 0.0), (1902.0, 2080.0)) (round trip Box2D((0.0, 0.0625), (1902.0, 2080.0)))) at gfx/wr/webrender/src/surface.rs:413

Reproduction: Put something very far down on a page, pinch-zoom in and out a few times.

Comment 1

[BugBot [:suhaib / :marco]]

:nical, since you are the author of the regressor, bug 2068160, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.

Comment 2

[Nicolas Silva [:nical]]

Attachment: Bug 2073850 - Scale the vis culling rect round-trip tolerance with the mapping translation. r=#gfx-reviewers

A picture cache slice that sits far from the origin (a large scroll or
pinch-zoom offset) cannot round-trip its culling rect through the f32
scale+offset exactly: unmap divides the screen by the mapping and map
multiplies it back, each rounding at the magnitude of the translation. In
the bug the loss is exactly one ulp (0.0625 at an offset of ~673405),
which is just past the fixed 0.05 tolerance, so the assertion fired because
of precision issue with the assertion itself rather than the invariant it
was trying to check.

I almost removed the assertion. It was added in an abundance of caution
to validate a complex change that was made recently but if it doesn't
uncover real issues for a month or two we should take it as signal that
the change was good and we don't need to keep checking it forever.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/e00f22e0c8bb
https://hg.mozilla.org/integration/autoland/rev/7f6fe90ce9f8
Scale the vis culling rect round-trip tolerance with the mapping translation. r=gfx-reviewers,gw

Comment 4

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/7f6fe90ce9f8